Treatment fluids comprising calcium aluminate cement and methods of use

ABSTRACT

Methods and systems for the treatment of wells are disclosed. A method for treating a well comprises providing a treatment fluid comprising calcium-aluminate cement, water, and a cement set retarder; and introducing the treatment fluid into a wellbore. A system for treating a well comprises a treatment fluid comprising calcium-aluminate cement, water, and a cement set retarder; a vessel to contain the treatment fluid; a pumping system coupled to the vessel to pump the treatment fluid; and a conduit coupled to the pumping system.

BACKGROUND

Methods of using treatment fluids and, more particularly, methods ofusing treatment fluids comprising calcium aluminate cement compositionsin well operations are provided.

Cement compositions may be used in a variety of subterranean operationsincluding operations that utilize treatment fluids. A broad variety ofcement compositions have been used as treatment fluids. In someinstances, extended-life cement compositions have been used. In contrastto conventional cement compositions that set and harden uponpreparation, extended-life cement compositions are characterized bybeing capable of remaining in a pumpable fluid state for at least aboutone day (e.g., about 7 days, about 2 weeks, about 2 years or more) atroom temperature (e.g., about 80° F.) in storage. When desired for use,the extended-life cement compositions should be capable of activationand consequently develop reasonable compressive strengths. For example,an extended-life cement composition that is activated may set into ahardened mass. Among other things, extended-life cement compositions maybe suitable for use in treatment fluids where it is desirable to preparethe treatment fluid in advance. This may allow the treatment fluid to bestored prior to use. In addition, this may allow the treatment fluid tobe prepared at a convenient location before transportation to the jobsite. Accordingly, capital expenditures may be reduced due to areduction in the need for on-site bulk storage and mixing equipment.This may be particularly useful for offshore operations where spaceonboard the vessels may be limited.

Drilling and fluid displacement are two subterranean operations thatutilize treatment fluids. Drilling requires the use of drilling fluid oras it is also known, drilling mud. Drilling fluids may be used tomaintain hydrostatic pressure in the wellbore, prevent formation damage,suspend cuttings, and to transport cuttings to the surface. Drillingfluids may be water-based or oil-based. Typical water-based drillingfluids may be composed of solely water or a mixture of water and varioustypes of clay. Oil based drilling fluids typically use a base fluid of apetroleum product.

Fluid displacement utilizes one or more fluids to displace another fluidfrom the wellbore. Typically this may be done to prevent contaminationof one fluid with another or the contamination of one fluid with theformation. A displacement fluid or as it is also known, a spacer fluid,may be water-based fluids. In most instances, spacer fluids may be usedto separate drilling fluid from a cement composition during a cementingoperation. Because the spacer fluid will be used to separate two otherfluids, such as the drilling fluid and the cement composition, thespacer fluid should be compatible with both treatment fluids.

Spotting fluids may be used to remove drilling fluid and prevent thedrilling fluid filter cake from interfering with subsequent primarycementing operations, this may be a potential problem where differentialsticking stops a drill pipe. A spofting fluid may be used to at leastpartially displacing the drilling fluid before the drilling fluid in thewellbore has had a chance to gain significant gel strength, for example,prior to introducing the pipe string into the well bore. Generally,these spotting fluids should not have an undesirable increase in gelstrength after being static in the wellbore for a period of time, forexample, up to at least two weeks, so that the spotting fluids may bedisplaced from the wellbore. After the wellbore is at least partiallyfilled with a spotting fluid, the pipe string to be cemented may beintroduced into the wellbore. When the cement composition is pumpedthrough the pipe string into the annulus, the drilling fluid (if any)and the spotting fluid in the pipe string and annulus may be displacedahead of the cement composition.

Switching between treatment fluids in a subterranean operation can becostly in both time and resources. Varied fluid types may requireseparate fluid storage, additional manpower, and additional equipment.In addition to the increased operating expenses, varied fluid use maycreate additional worksite problems such as higher environmentalburdens, fluid incompatibilities, and the inability to reuse fluids andmaterials once their respective portion of the operation has beencompleted.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings illustrate certain aspects of some of the examples of thepresent method and should not be used to limit or define the method.

FIG. 1 illustrates a system for preparation and delivery of a drillingfluid to a wellbore in accordance with certain examples.

FIG. 2 illustrates surface equipment that may be used in the placementof a displacement fluid in a wellbore in accordance with certainexamples.

FIG. 3 illustrates a method for displacing a prior pumped fluid using adisplacement fluid.

FIG. 4 illustrates the placement of a cement composition behind adisplacement fluid in a wellbore in accordance with certain examples.

FIG. 5A illustrates a method for placement of a spotting fluid into awellbore annulus in accordance with certain examples.

FIG. 5B illustrates a method for the placement of a spotting fluid intoa wellbore annulus in accordance with certain examples.

FIG. 5C illustrates a method for the placement of a spotting fluid intoa wellbore annulus in accordance with certain examples.

FIG. 5D illustrates a method for the placement of a spotting fluid intoa wellbore annulus in accordance with certain examples.

FIG. 6A illustrates a method for the placement of a spotting fluid intoa wellbore in accordance with certain examples.

FIG. 6B illustrates the placement of a pipe string into a wellboreannulus at least partially filled with a spotting fluid in accordancewith certain examples.

FIG. 7 illustrates a “right-angle” set profile of a treatment fluid inaccordance with certain examples.

DETAILED DESCRIPTION

Methods of using treatment fluids and, more particularly, methods ofusing treatment fluids comprising calcium aluminate cement compositionsin well operations are provided.

The treatment fluids may comprise calcium aluminate cement and water.Optionally, the treatment fluids may comprise a calcium-aluminate cementretarder, a cement-aluminate cement activator, a calcium-aluminatecement accelerator, and/or a dispersant. Advantageously, the treatmentfluids may be capable of remaining in a pumpable fluid state for anextended period of time, i.e., they may be capable of remaining in apumpable fluid state for at least about one day (e.g., about 7 days,about 2 weeks, about 2 years or more) at room temperature (e.g., about80° F.) in storage. Generally, the treatment fluids may developcompressive strength after activation. Advantageously, the treatmentfluids may develop reasonable compressive strengths at relatively lowtemperatures (e.g., temperatures of about 70° F. or less to about 140°F.). Thus, while the treatment fluids may be suitable for a number ofsubterranean cementing operations, they may be particularly suitable foruse in subterranean formations having relatively low bottom hole statictemperatures, e.g., temperatures of about 70° F. or less to about 140°F. Alternatively, the treatment fluids may be used in subterraneanformations having bottom hole static temperatures up to 450° F. orhigher.

The treatment fluids may comprise a calcium aluminate cement. Anycalcium aluminate cement may be suitable for use. Calcium aluminatecements may be described as cements that comprise calcium aluminates inan amount greater than 50% by weight of the dry calcium aluminate cement(i.e., the calcium aluminate cement before water or any additives areadded). A calcium aluminate may be defined as any calcium aluminateincluding, but not limited to, monocalcium aluminate, monocalciumdialuminate, tricalcium aluminate, dodecacalcium hepta-aluminate,monocalcium hexa-aluminate, dicalcium aluminate, pentacalciumtrialuminate, tetracalcium trialuminate, and the like. Where present,the calcium-aluminate cement may be included in the treatment fluids inan amount in the range of from about 40% to about 70% by weight of thetreatment fluids. For example, the calcium aluminate cement may bepresent in an amount ranging between any of and/or including any ofabout 40%, about 45%, about 50%, about 55%, about 60%, about 65%, orabout 70% by weight of the treatment fluids. One of ordinary skill inthe art, with the benefit of this disclosure, should recognize theappropriate amount of calcium-aluminate cement to include for a chosenapplication.

The treatment fluids may comprise water. The water may be from anysource provided that it does not contain an excess of compounds that mayundesirably affect other components in the treatment fluids, forexample, it may be important that no compounds in the water raise thealkalinity of the treatment fluids unless it is desirable to do so. Thewater may comprise fresh water or salt water. Salt water generally mayinclude one or more dissolved salts therein and may be saturated orunsaturated as desired for a particular application. Seawater or brinesmay be suitable for use in some applications. Further, the water may bepresent in an amount sufficient to form a pumpable fluid. In certainembodiments, the water may be present in the treatment fluids in anamount in the range of from about 33% to about 200% by weight of thecement (i.e., the weight of the calcium-aluminate cement). In certainembodiments, the water may be present in the treatment fluids in anamount in the range of from about 35% to about 70% by weight of thecement. With the benefit of this disclosure one of ordinary skill in theart should recognize the appropriate amount of water for a chosenapplication.

The treatment fluids may comprise a cement set retarder. Examples of thecement set retarder may include, but should not be limited, tohydroxycarboxylic acids such as citric, tartaric, gluconic acids ortheir respective salts, boric acid or its respective salt, andcombinations thereof. A specific example of a suitable cement setretarder is Fe-2™ Iron Sequestering Agent available from HalliburtonEnergy Services, Inc., Houston, Tex. Generally, the cement set retardermay be present in the treatment fluids in an amount sufficient to delaythe setting for a desired time. The cement set retarder may be presentin the treatment fluids in an amount in the range of from about 0.01% toabout 10% by weight of the cement (i.e., the calcium aluminate cement).More particularly, the cement set retarder may be present in an amountranging between any of and/or including any of about 0.01%, about 0.1%,about 1%, about 2%, about 4%, about 6%, about 8%, or about 10% by weightof the cement. Additionally, it is important to use cement set retardersthat do not undesirably affect the treatment fluids, for example, byincreasing the pH of the treatment fluids unless desired. One ofordinary skill in the art, with the benefit of this disclosure, shouldrecognize the appropriate amount of cement set retarder to include for achosen application.

The treatment fluids may optionally comprise a cement set activator ifit is desirable to induce setting of the treatment fluids. Certaincement set activators may additionally function as cement setaccelerators and may accelerate the development of compressive strengthin the treatment fluids in addition to activating the treatment fluids.A cement set activator may be any alkaline species that increases the pHof the treatment fluids sufficiently to initiate hydration reactions inthe calcium aluminate cement, but also does not otherwise interfere withthe setting of the calcium aluminate cement. Without being limited bytheory, it is believed that activation may be induced due to the cementset activator removing the hydration barrier caused by the cement setretarders in the treatment fluids. Moreover, the large exothermassociated with the setting of the calcium-aluminate cement is believedto provide a large enough temperature increase that the treatment fluidsmay be able to set at temperatures much lower than other types ofsettable treatment fluids. Potential examples of cement set activatorsmay include, but should not be limited to: Groups IA and IIA hydroxidessuch as lithium hydroxide, sodium hydroxide, magnesium hydroxide, andcalcium hydroxide; alkaline aluminates such as sodium aluminate;Portland cement, the like, and combinations thereof. Some of thetreatment fluids may benefit from the inclusion of two or more cementset activators or the combination of at least one cement set activatorand at least one cement set accelerator, whereas other treatment fluidsmay only require one cement set activator. With the benefit of thisdisclosure, one having ordinary skill in the art will be able to selectan appropriate cement set activator or combination of cement setactivators for use with a chosen application.

The cement set activator may be present in the treatment fluids in anamount in the range of from about 0.01% to about 10% by weight of thecement (i.e., the calcium-aluminate cement). More particularly, thecement set activator may be present in an amount ranging between any ofand/or including any of about 0.01%, about 0.1%, about 1%, about 2%,about 4%, about 6%, about 8%, or about 10% by weight of the cement.

As discussed above, the cement set activators may comprise calciumhydroxide which may be referred to as hydrated lime. As used herein, theterm “hydrated lime” will be understood to mean calcium hydroxide. Insome embodiments, the hydrated lime may be provided as quicklime(calcium oxide) which hydrates when mixed with water to form thehydrated lime. The hydrated lime may be included, for example, toactivate the calcium aluminate cement.

As discussed above, the cement set activator may comprise a Portlandcement. Examples of such Portland cements, include, but are not limitedto, Classes A, C, H, or G cements according to the American PetroleumInstitute, API Specification for Materials and Testing for Well Cements,API Specification 10, Fifth Ed., Jul. 1, 1990. In addition, the Portlandcement may include Portland cements classified as ASTM Type I, II, III,IV, or V. For some examples using Portland cement as a cement setactivator, it may be advantageous to also retard the Portland cementand/or activate a retarded Portland cement at various intervals duringuse of the methods disclosed herein. Any Portland cement set retarderand/or Portland cement set activator may be used in these instancesprovided that said Portland cement set retarders and/or Portland cementset activators do not undesirably interfere with the treatment fluids,for example, by prematurely increasing the pH of the treatment fluids.

The treatment fluids may optionally comprise a lithium salt which mayfunction as cement set accelerator. A cement set accelerator mayaccelerate the development of compressive strength once the calciumaluminate cement has been activated, but the cement set accelerator,unless otherwise noted, does not itself induce activation of the calciumaluminate cement. Examples of suitable lithium salts include, withoutlimitation, lithium sulfate and lithium carbonate. Without being limitedby theory, it is believed that the lithium ions increase the number ofnucleation sites for hydrate formation in the calcium aluminate cement.Thus, when the calcium aluminate cement is activated by combination withcement set activator, the presence of the lithium salts may acceleratethe development of compressive strength of the calcium aluminate cement.Preferably, the lithium salt should be added only to retarded or dormantcalcium aluminate cements. Introduction of a lithium salt to anon-retarded or non-dormant calcium aluminate cement may undesirablyaccelerate setting of the calcium-aluminate cement, dependent upon thespecific calcium-aluminate cement used and the other components in thetreatment fluids. However, lithium salts added to retarded or dormantcalcium-aluminate cements may prevent this risk. The lithium salt may beincluded in the treatment fluids in an amount in the range of about0.01% to about 10% by weight of the cement (i.e., the weight of thecalcium-aluminate cement). More particularly, the lithium salt may bepresent in an amount ranging between any of and/or including any ofabout 0.01%, about 0.1%, about 0.5%, about 1%, about 2%, about 3%, about4%, about 5%, or about 10% by weight of the cement. One of ordinaryskill in the art, with the benefit of this disclosure, should recognizethe appropriate amount of lithium salt to include for a chosenapplication.

As previously mentioned, the treatment fluids may optionally comprise adispersant. Examples of suitable dispersants may include, withoutlimitation, sulfonated-formaldehyde-based dispersants (e.g., sulfonatedacetone formaldehyde condensate), examples of which may include Daxad®19 dispersant available from Geo Specialty Chemicals, Ambler, Pa.Additionally, polyoxyethylene phosphonates and polyox polycarboxylatesmay be used. Other suitable dispersants may be polycarboxylated etherdispersants such as Liquiment® 5581F and Liquiment® 514L dispersantsavailable from BASF Corporation Houston, Tex.; or Ethacryl™ G dispersantavailable from Coatex, Genay, France. An additional example of asuitable commercially available dispersant is CFR′-3 dispersant,available from Halliburton Energy Services, Inc., Houston, Tex. TheLiquiment® 514L dispersant may comprise 36% by weight of thepolycarboxylated ether in water. While a variety of dispersants may beused, some dispersants may be preferred for use with specific cement setretarders. Additionally, it is important to use dispersants that do notundesirably affect the treatment fluids, for example, by inducingpremature setting. One of ordinary skill in the art, with the benefit ofthis disclosure, should recognize the appropriate type of dispersant toinclude for a chosen application.

The dispersant may be included in the treatment fluids in an amount inthe range of from about 0.01% to about 5% by weight of the cement (i.e.,the weight of the calcium-aluminate cement). More particularly, thedispersant may be present in an amount ranging between any of and/orincluding any of about 0.01%, about 0.1%, about 0.5%, about 1%, about2%, about 3%, about 4%, or about 5% by weight of the cement. One ofordinary skill in the art, with the benefit of this disclosure, willrecognize the appropriate amount of dispersant to include for a chosenapplication.

The treatment fluids may optionally comprise a filler material. Thefiller material used for the treatment fluids may comprise any suitablefiller material provided the filler material does not raise thealkalinity of the treatment fluids as this may induce the prematuresetting of the treatment fluids. Without limitation, the filler materialmay include silica, sand, fly ash, or silica fume. Generally, the fillermaterial may be present in the treatment fluids in an amount sufficientto make the system economically competitive. The filler material may bepresent in the treatment fluids in an amount in the range of from about0.01% to about 100% by weight of the cement (i.e., the calcium aluminatecement). More particularly, the filler material may be present in anamount ranging between any of and/or including any of about 0.01%, about0.1%, about 1%, about 10%, about 25%, about 50%, about 75%, or about100% by weight of the cement. One of ordinary skill in the art, with thebenefit of this disclosure, should recognize the appropriate amount offiller material to include for a chosen application.

The treatment fluids may optionally comprise a viscosifier. Theviscosifier may be included to optimize fluid rheology and to stabilizethe suspension. Without limitation, examples of viscosifiers includesynthetic polymers; swellable clays such as bentonite; inorganicparticulates such as microsand, glass beads, and/or manganese oxide; orbiopolymers such as cellulose derivatives (e.g., hydroxyethyl cellulose,carboxymethyl cellulose, carboxymethyl hydroxyethyl cellulose). Anexample of a commercially available viscosifier is SA-1015™ availablefrom Halliburton Energy Services, Inc., Houston, Tex. The viscosifiermay be included in the treatment fluids in an amount in the range offrom about 0.01% to about 0.5% by weight of the cement (i.e., thecalcium aluminate cement). In specific embodiments, the viscosifier maybe present in an amount ranging between any of and/or including any ofabout 0.01%, about 0.05%, about 0.1%, about 0.2%, about 0.3%, about0.4%, or about 0.5% by weight of the cement. One of ordinary skill inthe art, with the benefit of this disclosure, will recognize theappropriate amount of viscosifier to include for a chosen application.

Other additives suitable for use in well operations also may be added tothe treatment fluids as deemed appropriate by one of ordinary skill inthe art. Examples of such additives include, but are not limited to,strength-retrogression additives, set weighting agents, lightweightadditives, gas-generating additives, mechanical property enhancingadditives, lost-circulation materials, defoaming agents, foaming agents,thixotropic additives, and combinations thereof. Specific examples ofthese, and other additives include silica (e.g., crystalline silica,amorphous silica, fumed silica, etc.), salts, fibers, hydratable clays,shale (e.g., calcined shale, vitrified shale, etc.), microspheres,diatomaceous earth, natural pozzolan, resins, latex, combinationsthereof, and the like. Other optional additives may also be included,including, but not limited to, cement kiln dust, lime kiln dust, flyash, slag cement, shale, zeolite, metakaolin, pumice, perlite, lime,silica, rice husk ash, small-particle size cement, combinations thereof,and the like. A person having ordinary skill in the art, with thebenefit of this disclosure, will be able to determine the type andamount of additive useful for a particular application and desiredresult.

Strength-retrogression additives may be included in the treatment fluidsto, for example, prevent the retrogression of strength after thetreatment fluids have been allowed to develop compressive strength.These additives may allow the treatment fluids to form as intended,preventing cracks and premature failure. Examples of suitablestrength-retrogression additives may include, but are not limited to,amorphous silica, coarse grain crystalline silica, fine graincrystalline silica, or a combination thereof.

Weighting agents are typically materials that weigh more than water andmay be used to increase the density of the treatment fluids. By way ofexample, weighting agents may have a specific gravity of about 2 orhigher (e.g., about 2, about 4, etc.). Examples of weighting agents thatmay be used include, but are not limited to, hematite, hausmannite, andbarite, and combinations thereof. Specific examples of suitableweighting agents include HI-DENSE® weighting agent, available fromHalliburton Energy Services, Inc.

Lightweight additives may be included in the treatment fluids to, forexample, decrease the density of the treatment fluids. Examples ofsuitable lightweight additives include, but are not limited to,bentonite, coal, diatomaceous earth, expanded perlite, fly ash,gilsonite, hollow microspheres, low-density elastic beads, nitrogen,pozzolan-bentonite, sodium silicate, combinations thereof, or otherlightweight additives known in the art.

Gas-generating additives may be included in the treatment fluids torelease gas at a predetermined time, which may be beneficial to preventgas migration from the formation through the treatment fluids beforethey hardens. The generated gas may combine with or inhibit thepermeation of the treatment fluids by formation gas. Examples ofsuitable gas-generating additives include, but are not limited to, metalparticles (e.g., aluminum powder) that react with an alkaline solutionto generate a gas.

Mechanical-property-enhancing additives may be included in the treatmentfluids to, for example, ensure adequate compressive strength andlong-term structural integrity. These properties can be affected by thestrains, stresses, temperature, pressure, and impact effects from asubterranean environment. Examples of mechanical property enhancingadditives include, but are not limited to, carbon fibers, glass fibers,metal fibers, mineral fibers, silica fibers, polymeric elastomers, andlatexes.

Lost-circulation materials may be included in the treatment fluids to,for example, help prevent the loss of fluid circulation into thesubterranean formation. Examples of lost-circulation materials includebut are not limited to, cedar bark, shredded cane stalks, mineral fiber,mica flakes, cellophane, calcium carbonate, ground rubber, polymericmaterials, pieces of plastic, grounded marble, wood, nut hulls, plasticlaminates (Formica® laminate), corncobs, and cotton hulls.

Defoaming additives may be included in the treatment fluids to, forexample, reduce the tendency of the treatment fluids to foam duringmixing and pumping of the treatment fluids. Examples of suitabledefoaming additives include, but are not limited to, polyol siliconecompounds. Suitable defoaming additives are available from HalliburtonEnergy Services, Inc., under the product name D-AIR™ defoamers.

Foaming additives (e.g., foaming surfactants) may be included in thetreatment fluids to, for example, facilitate foaming and/or stabilizethe resultant foam formed therewith. Examples of suitable foamingadditives include, but are not limited to: mixtures of an ammonium saltof an alkyl ether sulfate, a cocoamidopropyl betaine surfactant, acocoamidopropyl dimethylamine oxide surfactant, sodium chloride, andwater; mixtures of an ammonium salt of an alkyl ether sulfatesurfactant, a cocoamidopropyl hydroxysultaine surfactant, acocoamidopropyl dimethylamine oxide surfactant, sodium chloride, andwater; hydrolyzed keratin; mixtures of an ethoxylated alcohol ethersulfate surfactant, an alkyl or alkene amidopropyl betaine surfactant,and an alkyl or alkene dimethylamine oxide surfactant; aqueous solutionsof an alpha-olefinic sulfonate surfactant and a betaine surfactant; andcombinations thereof. An example of a suitable foaming additive isZONESEALANT™ 2000 agent, available from Halliburton Energy Services,Houston, Tex.

Thixotropic additives may be included in the treatment fluids to, forexample, provide a treatment fluid that may be pumpable as a thin or lowviscosity fluid, but when allowed to remain quiescent attains arelatively high viscosity. Among other things, thixotropic additives maybe used to help control free water, create rapid gelation as thetreatment fluids set, combat lost circulation, prevent “fallback” inannular column, and minimize gas migration. Examples of suitablethixotropic additives include, but are not limited to, gypsum, watersoluble carboxyalkyl, hydroxyalkyl, mixed carboxyalkyl hydroxyalkyleither of cellulose, polyvalent metal salts, zirconium oxychloride withhydroxyethyl cellulose, or a combination thereof.

Those of ordinary skill in the art will appreciate that embodiments ofthe treatment fluids generally should have a density suitable for aparticular application. By way of example, the treatment fluids may havea density in the range of from about 4 pounds per gallon (“lb/gal”) toabout 20 lb/gal. In certain embodiments, the treatment fluids may have adensity in the range of from about 8 lb/gal to about 17 lb/gal.Embodiments of the treatment fluids may be foamed or unfoamed or maycomprise other means to reduce their densities, such as hollowmicrospheres, low-density elastic beads, or other density-reducingadditives known in the art. In embodiments, the density may be reducedafter storage, but prior to placement in a subterranean formation. Inembodiments, weighting additives may be used to increase the density ofthe treatment fluids. Examples of suitable weighting additives mayinclude barite, hematite, hausmannite, calcium carbonate, siderite,ilmenite, or combinations thereof. In particular embodiments, theweighting additives may have a specific gravity of 3 or greater. Thoseof ordinary skill in the art, with the benefit of this disclosure, willrecognize the appropriate density required for a particular application.

As previously mentioned, when it is desirable for the treatment fluidsto set, the treatment fluids may have a delayed set in that they may becapable of remaining in a pumpable fluid state for at least one day(e.g., about 1 day, about 2 weeks, about 2 years or more) at roomtemperature (e.g., about 80° F.) in storage. For example, the treatmentfluids may remain in a pumpable fluid state for a period of time fromabout 1 day to about 7 days or more. In some embodiments, the treatmentfluids may remain in a pumpable fluid state for at least about 1 day,about 7 days, about 10 days, about 20 days, about 30 days, about 40days, about 50 days, about 60 days, or longer. A fluid is considered tobe in a pumpable fluid state where the fluid has a consistency of lessthan 70 Bearden units of consistency (“Bc”), as measured on apressurized consistometer in accordance with the procedure fordetermining cement thickening times set forth in API RP Practice 10B-2,Recommended Practice for Testing Well Cements, First Edition, July 2005.

As discussed above, when setting is desirable, the treatment fluids maybe activated (e.g., by addition of a cement set activator) to set into ahardened mass. The term “activate”, as used herein, refers to theactivation of any calcium aluminate cement in the treatment fluids andin certain cases may also refer to the acceleration of the setting ofany calcium aluminate cement in the treatment fluids, if the mechanismof said activation also accelerates the development of compressivestrength. By way of example, a cement set activator may be added to atreatment fluid to activate the treatment fluid. A treatment fluid thathas been activated may set to form a hardened mass in a time period inthe range of from about 1 hour to about 12 days. For example,embodiments of the treatment fluids may set to form a hardened mass in atime period ranging between any of and/or including any of about 1 hour,about 6 hours, about 12 hours, about 1 day, about 2 days, about 4 days,about 6 days, about 8 days, about 10 days, or about 12 days.

The treatment fluids may set to have a desirable compressive strengthafter activation. Compressive strength is generally the capacity of amaterial or structure to withstand axially directed pushing forces. Thecompressive strength may be measured at a specified time after theactivation of the calcium aluminate cement while the treatment fluid ismaintained under specified temperature and pressure conditions.Compressive strength can be measured by either destructive ornon-destructive methods. The destructive method physically tests thestrength of treatment fluid samples at various points in time bycrushing the samples in a compression-testing machine. The compressivestrength is calculated from the failure load divided by thecross-sectional area resisting the load and is reported in units ofpound-force per square inch (psi). Non-destructive methods may employ aUCA™ Ultrasonic Cement Analyzer, available from Fann Instrument Company,Houston, Tex. Compressive strength values may be determined inaccordance with API RP 10B-2, Recommended Practice for Testing WellCements, First Edition, July 2005.

By way of example, the treatment fluids may develop a 24-hourcompressive strength in the range of from about 50 psi to about 5000psi, alternatively, from about 100 psi to about 4500 psi, oralternatively from about 500 psi to about 4000 psi. In particular, thetreatment fluids may develop a compressive strength in 24 hours of atleast about 50 psi, at least about 100 psi, at least about 500 psi, ormore. The compressive strength values may be determined usingdestructive or non-destructive methods at any temperature, howevercompressive strength development at temperatures ranging from 70° F. to140° F. may be of particular importance for potential use insubterranean formations having relatively low bottom hole statictemperatures.

In some examples, the treatment fluids may have desirable thickeningtimes. Thickening time typically refers to the time a fluid, such as atreatment fluid, remains in a fluid state capable of being pumped. Anumber of different laboratory techniques may be used to measurethickening time. A pressurized consistometer, operated in accordancewith the procedure set forth in the aforementioned API RP Practice10B-2, may be used to measure whether a fluid is in a pumpable fluidstate. The thickening time may be the time for the treatment fluid toreach 70 Bc and may be reported as the time to reach 70 Bc. Thetreatment fluids may have thickening times greater than about 1 hour,alternatively, greater than about 2 hours, greater than about 15 hours,greater than about 30 hours, greater than about 100 hours, oralternatively greater than about 190 hours at 3,000 psi and temperaturesin a range of from about 50° F. to about 400° F., alternatively, in arange of from about 70° F. to about 140° F., and alternatively at atemperature of about 100° F. As will be illustrated in the examplesbelow, thickening times may be controlled by the degree to which the pHof the treatment fluid is increased. This is related, to a degree, tothe concentration of the cement set activator and allows for aquantitative method of controlling the set time of the treatment fluids.

The treatment fluids described above may be used in a variety ofapplications. For example, the treatment fluids disclosed herein may beused as a drilling fluid for drilling a wellbore in a subterraneanformation by circulating a treatment fluid while drilling a wellbore incontact with a drill bit and a subterranean formation. After thetreatment fluids are used to drill a wellbore in a subterraneanformation, a casing may be placed within the wellbore. If desired, allor a portion of the treatment fluid may be permitted to set behind thecasing.

A method of treating a well may be provided. The method may include oneor all of the components and/or steps illustrated in FIGS. 1-7. Themethod may comprise providing a treatment fluid comprisingcalcium-aluminate cement, water, and a cement set retarder; andintroducing the treatment fluid into a wellbore. The step of introducingthe treatment fluid into the wellbore may comprise introducing thetreatment fluid into the wellbore while a drill bit is present in thewellbore. The step of introducing the treatment fluid into the wellboremay displace at least a portion of a drilling fluid from the wellbore.At least a portion of the treatment fluid may be recovered and used as adrilling fluid, a displacement fluid, a spotting fluid, a cement, or acombination thereof. The method may further comprise the steps ofrecovering at least a portion of the treatment fluid; activating saidportion of the treatment fluid with a cement set activator; and placingthe activated treatment fluid into the wellbore. At least a portion ofthe treatment fluid may be allowed to remain in the wellbore. At least aportion of the treatment fluid may be allowed to set behind a conduitplaced into the wellbore. At least a portion of the treatment fluid maybe allowed to remain static in the wellbore, and the treatment fluid mayremain in a pumpable fluid state for a period of about 1 day or longerwhile static in the wellbore. The treatment fluid may be introduced intothe wellbore such that the treatment fluid forms a puddle in the bottomof the wellbore, said method may further comprise the steps of placing aconduit into the puddle formed by the treatment fluid in the bottom ofthe wellbore; and inducing the treatment fluid to set in an annulussurrounding the conduit. The cement set retarder may be selected fromthe group consisting of hydroxycarboxylic acids or their respectivesalts, boric acid or its respective salt, and any combination thereof.The treatment fluid may further comprise a cement set activator selectedfrom the group consisting of Groups IA and IIA hydroxides; alkalinealuminates; Portland cement, and combinations thereof. The treatmentfluid may further comprise a cement set accelerator selected from thegroup consisting of lithium sulfate, lithium carbonate, and anycombination thereof.

A system of treating a well may be provided. The system may include oneor all of the components illustrated in FIGS. 1-7. The system maycomprise a treatment fluid comprising calcium-aluminate cement, water,and a cement set retarder; a vessel to contain the treatment fluid; apumping system coupled to the vessel to pump the treatment fluid; and aconduit coupled to the pumping system. The system may further comprise astorage system for storing the treatment fluid. The system may furthercomprise a drilling system for drilling a wellbore. The system mayfurther comprise a treatment fluid recovery system for recovering atleast a portion of the treatment fluid from a wellbore. The cement setretarder may be selected from the group consisting of hydroxycarboxylicacids or their respective salts, boric acid or its respective salt, andany combination thereof. The treatment fluid may further comprise acement set activator selected from the group consisting of Groups IA andIIA hydroxides; alkaline aluminates; Portland cement, and combinationsthereof. The treatment fluid may further comprise a dispersant selectedfrom the group consisting of sulfonated-formaldehyde-based dispersant, apolycarboxylated ether dispersant, and any combination thereof. Thetreatment fluid may further comprise a cement set accelerator selectedfrom the group consisting of lithium sulfate, lithium carbonate, and anycombination thereof.

The example treatment fluids disclosed herein may directly or indirectlyaffect one or more components or pieces of equipment associated with thepreparation, delivery, recapture, recycling, reuse, and/or disposal ofthe disclosed treatment fluids. Any of the treatment fluids describedherein may be contained within a vessel and/or any type of sufficientstorage system. Without limitation, examples of such vessels, mayinclude mud pits, barrels, mixers, drums, trucks, storage containers,etc. Some of the example vessels may comprise mixing equipment, forexample, baffles. Any of the vessel examples may be coupled to any ofthe pumps, pumping systems, conduits, or fluid recovery systemsdisclosed herein. Any of the pumps, pumping systems, or conduitsdisclosed herein may be coupled to one another as well as any otherupstream or downstream system or equipment, such as vessels, storagesystems. Fluid recovery systems, and the like. Further, fluid recoverysystems comprising vessels and/or pumping systems may be used torecovery any of the treatment fluids described herein. These recoveredtreatment fluids may be reconditioned and recycled, may be stored (e.g.,using a storage system or vessel), or may simply be reused.

The treatment fluids disclosed herein may be used as a drilling fluid.The drilling fluids used herein comprise the formulations of thedisclosed treatment fluids discussed above. The disclosed treatmentfluids may be used to aid in the drilling of a wellbore, e.g., bycirculating drill cuttings back to the surface via the annulus betweenthe drill string and the walls of the wellbore. If desired, the drillingfluid may be permitted to set behind the casing.

With reference to FIG. 1, the disclosed treatment fluids may directly orindirectly affect one or more components or pieces of equipmentassociated with an example wellbore drilling assembly 100. It should benoted that while FIG. 1 generally depicts a land-based drillingassembly, those skilled in the art will readily recognize that theprinciples described herein are equally applicable to subsea drillingoperations that employ floating or sea-based platforms and rigs, withoutdeparting from the scope of the disclosure.

As illustrated, the drilling assembly 100 may include a drillingplatform 102 that supports a derrick 104 having a traveling block 106for raising and lowering a drill string 108. The drill string 108 mayinclude, but is not limited to, conduits such as drill pipe and coiledtubing, as generally known to those skilled in the art. A kelly 110supports the drill string 108 as it is lowered through a rotary table112. A drill bit 114 is attached to the distal end of the drill string108 and is driven either by a downhole motor and/or via rotation of thedrill string 108 from the well surface. As the bit 114 rotates, itcreates a borehole 116 that penetrates various subterranean formations118.

A pump 120 (e.g., a mud pump) circulates drilling fluid 122, which mayhave been stored in a vessel prior to use, comprising at least one ofthe treatment fluids disclosed herein, through a feed pipe 124 and tothe kelly 110, which conveys the drilling fluid 122 downhole through theinterior of the drill string 108 and through one or more orifices in thedrill bit 114. The pump 120 may be part of a pumping system. Thedrilling fluid 122 is then circulated back to the surface via an annulus126 defined between the drill string 108 and the walls of the borehole116. At the surface, the recirculated or spent drilling fluid 122 exitsthe annulus 126 and may be conveyed to one or more fluid processingunit(s) 128 via an interconnecting flow line 130. After passing throughthe fluid processing unit(s) 128, a “cleaned” drilling fluid 122 isdeposited into a nearby retention pit 132 (i.e., a mud pit), which mayfunction as a vessel or storage system for the drilling fluid. Whileillustrated as being arranged at the outlet of the wellbore 116 via theannulus 126, those skilled in the art will readily appreciate that thefluid processing unit(s) 128 may be arranged at any other location inthe drilling assembly 100 to facilitate its proper function, withoutdeparting from the scope of the scope of the disclosure. In alternativeexamples, at least a portion of the drilling fluid 122 may be leftbehind in the wellbore, and optionally the calcium aluminate cement inthe drilling fluid may be activated with a cement set activator andallowed to set behind the casing. In further optional examples, at leasta portion of the drilling fluid 122 may be recovered and used as anothertreatment fluid, for example, as a displacement fluid, spotting fluid, acement, or the like.

The drilling fluid 122 may be added to a mixing hopper 134, a type ofvessel, communicably coupled to or otherwise in fluid communication withthe retention pit 132. The mixing hopper 134 may include, but is notlimited to, mixers and related mixing equipment known to those skilledin the art. In alternative embodiments, however, the drilling fluid 122may not be added to a mixing hopper. In at least one example, therecould be more than one retention pit 132, such as multiple retentionpits 132 in series. Moreover, the retention pit 132 may berepresentative of one or more fluid storage facilities and/or unitswhere the disclosed treatment fluids may be stored, reconditioned,and/or regulated until used as a treatment fluid, for example, as adrilling fluid 122.

As mentioned above, the drilling fluid 122 may directly or indirectlyaffect the components and equipment of the drilling assembly 100. Forexample, the drilling fluid may directly or indirectly affect the fluidprocessing unit(s) 128 which may include, but is not limited to, one ormore of a shaker (e.g., shale shaker), a centrifuge, a hydrocyclone, aseparator (including magnetic and electrical separators), a desilter, adesander, a separator, a filter (e.g., diatomaceous earth filters), aheat exchanger, any fluid reclamation equipment. The fluid processingunit(s) 128 may further include one or more sensors, gauges, pumps,compressors, and the like used store, monitor, regulate, and/orrecondition the treatment fluids.

The disclosed drilling fluids may directly or indirectly affect the pump120 and any pumping systems, which representatively includes anyconduits, pipelines, trucks, tubulars, and/or pipes which may be coupledto the pump and/or any pumping systems and may be used to fluidicallyconvey the drilling fluid downhole, any pumps, compressors, or motors(e.g., topside or downhole) used to drive the drilling fluid intomotion, any valves or related joints used to regulate the pressure orflow rate of the drilling fluid, and any sensors (i.e., pressure,temperature, flow rate, etc.), gauges, and/or combinations thereof, andthe like. The disclosed drilling fluids may also directly or indirectlyaffect the mixing hopper 134 and the retention pit 132 and theirassorted variations.

The disclosed drilling fluids may also directly or indirectly affect thevarious downhole equipment and tools that may come into contact with thedrilling fluids such as, but not limited to, the drill string 108, anyfloats, drill collars, mud motors, downhole motors and/or pumpsassociated with the drill string 108, and any MWD/LWD tools and relatedtelemetry equipment, sensors or distributed sensors associated with thedrill string 108. The disclosed drilling fluids may also directly orindirectly affect any downhole heat exchangers, valves and correspondingactuation devices, tool seals, packers and other wellbore isolationdevices or components, and the like associated with the wellbore 116.The drilling fluids may also directly or indirectly affect the drill bit114, which may include, but is not limited to, roller cone bits, PDCbits, natural diamond bits, any hole openers, reamers, coring bits, etc.

While not specifically illustrated herein, the drilling fluids may alsodirectly or indirectly affect any transport or delivery equipment usedto convey the drilling fluids to the drilling assembly 100 such as, forexample, any transport vessels, conduits, pipelines, trucks, tubulars,and/or pipes used to fluidically move the drilling fluids from onelocation to another, any pumps, compressors, or motors used to drive thedrilling fluids into motion, any valves or related joints used toregulate the pressure or flow rate of the drilling fluids, and anysensors (i.e., pressure and temperature), gauges, and/or combinationsthereof, and the like.

The treatment fluids disclosed herein may also be used as a displacementor spacer fluid. The displacement fluids used herein comprise theformulations of the disclosed treatment fluids discussed above. Thedisclosed treatment fluids may be used to displace a drilling mud orother treatment fluid, e.g., by circulating a displacement fluidcomprising at least one of the treatment fluids disclosed herein back tothe surface via the annulus between the drill string and the walls ofthe wellbore. As the displacement fluid is circulated back to thesurface, it displaces any prior placed fluids remaining in the wellbore.If desired, the displacement fluid may be permitted to set behind thecasing.

The density of the displacement fluids may be adjusted by the additionof water and/or a viscosifier. The water and/or viscosifier may be addedin any amount to achieve the appropriate density for a rheologicalhierarchy for a given application. An example of a suitable viscosifieris SA-1015™ suspending agent available from Halliburton Energy Services,Houston, Tex. Additionally, light weight and heavy weight agents mayalso be added to adjust the density as is appropriate to maintain therheological hierarchy. One of ordinary skill in the art, with thebenefit of this disclosure, will recognize the appropriate density andmethod of density adjustment necessary for a chosen application.

The displacement fluids may also be foamed with a foaming additiveand/or a gas, for example, to provide a displacement fluid with areduced density. The gas used for foaming the displacement fluid may beany suitable gas for foaming, including, but not limited to: air,nitrogen, and combinations thereof. Generally, the gas should be in anamount sufficient to form the desired foam. Foaming additives may beincluded in embodiments to, for example, facilitate foaming and/orstabilize the resultant foam formed therewith. Examples of suitablefoaming additives include, but are not limited to: mixtures of anammonium salt of an alkyl ether sulfate, a cocoamidopropyl betainesurfactant, a cocoamidopropyl dimethylamine oxide surfactant, sodiumchloride, and water; mixtures of an ammonium salt of an alkyl ethersulfate surfactant, a cocoamidopropyl hydroxysultaine surfactant, acocoamidopropyl dimethylamine oxide surfactant, sodium chloride, andwater; hydrolyzed keratin; mixtures of an ethoxylated alcohol ethersulfate surfactant, an alkyl or alkene amidopropyl betaine surfactant,and an alkyl or alkene dimethylamine oxide surfactant; aqueous solutionsof an alpha-olefinic sulfonate surfactant and a betaine surfactant; andcombinations thereof. An example of a suitable foaming additive isZONESEALANT™ 2000 agent, available from Halliburton Energy Services,Houston, Tex.

Referring now to FIG. 2, a fluid handling system 200 is illustrated. Adisplacement fluid comprising at least one of the treatment fluidsdisclosed herein may be mixed in mixing equipment 205, such as a mixer,recirculating tub, or any type of vessel comprising mixing equipment,and then pumped via pump 210 or any type of pumping system to the wellbore. As illustrated in FIG. 3, the displacement fluid and anysubsequent fluid (e.g., a cement composition) may be pumped into thecasing 215 in the direction shown by the arrows. The displacement fluidmay be pumped through the casing 215, a type of conduit, and through orinto the subterranean formation 220 until it reaches the end point andis pushed upward into the annulus 225 which resides between the pipecasing 215 and walls 230 of well bore 235. The displacement fluid maydisplace any prior pumped fluid (e.g., a drilling fluid) and may alsoseparate any subsequently pumped fluid (e.g., a cement composition). Ifdesired, at least a portion of the displacement fluid may be left behindin the wellbore and optionally the calcium aluminate cement in thedisplacement fluid may be activated with a cement set activator andallowed to set behind the casing. In further optional examples, at leasta portion of the displacement fluid may be recovered and used as anothertreatment fluid, for example, as a drilling fluid, spotting fluid, acement, or the like. The recovered treatment fluid may be recoveredusing a recovery system and optionally a storage system, said systemsmay comprise some of the equipment discussed above, for example vessels,pumps, conduits, etc.

FIG. 4 illustrates a displacement fluid that has been allowed to remainin a wellbore after displacing a drilling fluid from the wellbore andafter subsequent pumping of a cement composition into the wellbore.Cement composition 245 is pumped downhole so that the cement composition245 is disposed between the walls 230 of the wellbore 235 and the casing215. As illustrated, the displacement fluid 250 may be disposed in thewellbore 235 above the cement composition 245. The displacement fluid250 may be disposed between the walls 230 of the wellbore 235 and thecasing 215. The displacement fluid 250 may be allowed to remain betweenthe walls 230 of the wellbore 235 and the casing 215 if desired.Additionally, displacement fluid 250 may be allowed to set into ahardened mass between the walls 230 of the wellbore 235 and the casing215. Setting of the displacement fluid 250 may be induced throughcontact with a cement set activator or any such sufficient method ofactivation.

The treatment fluids disclosed herein may also be used as a spottingfluid. The spotting fluids used herein comprise the formulations of thedisclosed treatment fluids discussed above. The disclosed spottingfluids may be used to displace a drilling mud or other treatment fluidin a typical spotting fluid operation, for example, to free adifferentially stuck pipe or in other types of spotting fluidapplications such as “puddle jobs.” As related to the disclosure abovedetailing the drilling fluid applications and displacement fluidapplications, if desired, at least a portion of the spotting fluid,which comprises at least one of the treatment fluids disclosed herein,may be left behind in the wellbore to set into a hardened mass. Infurther optional examples, at least a portion of the spotting fluid maybe recovered and used as another treatment fluid, for example, as adrilling fluid, displacement fluid, a cement, or the like.

An example of using a treatment fluid comprising a spotting fluid willnow be described with reference to FIGS. 5A-5D. The spotting fluid maybe pumped into the wellbore using any sufficient means, for example, themeans described above for pumping the drilling fluids and displacementfluids. FIG. 5A depicts subterranean formation 300 penetrated bywellbore 305 with drilling fluid 310 disposed therein. While thewellbore 305 is shown extending generally vertically into thesubterranean formation 300, the principles described herein are alsoapplicable to wellbores that extend at an angle through the subterraneanformation 300, such as horizontal and slanted wellbores. The wellbore305 may be drilled into the subterranean formation 300 using anysuitable drilling technique. As illustrated, the drilling fluid 310 maybe introduced into the wellbore 305 through a drill string and bottomhole assembly 315. On the walls 320 of the wellbore 305 may be foundpockets 325 which may have been created from washouts, fractures,crevices and/or otherwise naturally occurring features of thesubterranean formation 300. A spotting fluid 330 may be run behind thedrilling fluid 310, which occupies the lower portion of the drill stringand bottom hole assembly 315.

FIG. 5B depicts the subterranean formation 300 with the drill string andbottom hole assembly 315 still placed downhole, and the spotting fluid330 circulated through the drill string and bottom hole assembly 315such that it exits the drill string and bottom hole assembly 315 andtravels upward through the annulus 335 between the drill string andbottom hole assembly 315 and the walls 320 of wellbore 305, thusdisplacing the drilling fluid 310. At least a portion of the displaceddrilling fluid 310 may exit the annulus 335 via a flow line and bedeposited, for example, in one or more retention pits (e.g., a mud pit).While the spotting fluid 330 is exiting the drill string and bottom holeassembly 315 downhole, the drill string and bottom hole assembly 315 maybe circulated and reciprocated in a manner that improves removal of thedrilling fluid 310 trapped along the wellbore walls 320 and in thepockets 325.

As shown in FIG. 5C, after the drilling fluid 310 is displaced by thespotting fluid 330, the drill string and bottom hole assembly 315 may beremoved and a casing string 340 may be placed into the wellbore 305. Acement composition 345 may then be run behind the spotting fluid 330 inthe casing string 340, and, as depicted in FIG. 5D, circulated throughthe casing string 340 such that it exits the bottom of the casing string340 and travels upward through the annulus 335 between the casing string340 and the walls 320 of the wellbore 305 to the predeterminedtop-of-cement depth. If desired, any of the spotting fluid 330 that isnot displaced and remains on the walls 320 of the wellbore 305 and/or inthe pockets 325, may be induced to set into a hardened mass 350,therefore precluding the formation of undesirable channels and pathwaysthrough which fluids may migrate.

An example of using a spotting fluid 330 in a “puddle job” operationwill now be described with reference to FIGS. 6A and 6B. Referring nowto FIG. 6A, the wellbore 305 is illustrated penetrating subterraneanformation 300. A casing string 340 may be run into the wellbore 305 to adepth placing the lower end of the casing string 340 to be cementedabove the critical interval through which a cement sheath is desired.Mounted on the lower end of the casing string 340 may be a float valve355 or any other type of plug (e.g., any sufficient sealing plug and notnecessarily a valve). In embodiments, the float valve 355 may be a floatvalve of any type (e.g., a flapper float valve). The casing string 340may have centralizers 360 (e.g., as shown on FIG. 6B) along its lengthto keep the casing string 340 away from the walls 320 of the wellbore305.

The spotting fluid 330 may be pumped and discharged into the lower endof the wellbore 305. The spotting fluid 330 may be discharged into thelower end of the wellbore 305 via a drill string and bottom holeassembly 315 (e.g., as shown in FIGS. 5A and 5B) which may be placedinto the wellbore 305 prior to positioning the casing string 340 intothe wellbore 305. Alternatively, the spotting fluid 330 may bedischarged into the lower end of the wellbore 305 via a drill string andbottom hole assembly 315 (or other suitable conduit) that is run throughthe casing string 340 such that the drill string and bottom holeassembly 315 exit through the lower end of the casing string 340 via thefloat valve 355. The volume of the spotting fluid 330 pumped into thewellbore 305 may depend on a number of factors, including the length ofthe interval needed to be set. For example, the spotting fluid 330 mayremain in a pumpable fluid state (i.e., the spotting fluid has aconsistency of less than 70 Bc) for a period of 1 day, 3 days, 7 day, orlonger. In practice, the spotting fluid 330 should not set in thewellbore 305 until all operations requiring the spotting fluid 330 toremain in a pumpable fluid state have been completed. It is thereforebeneficial to have an accurate estimate of the duration of suchoperations prior to the formulation of the spotting fluid 330 and toavoid contacting the spotting fluid 330 with any material which mayinduce premature setting such as materials which may increase the pH ofspotting fluid 330.

Turning now to FIG. 6B, after the desired volume of the spotting fluid330 has been discharged into the wellbore 305, the casing string 340 maybe lowered to the desired depth within the wellbore 305. As illustrated,the casing string 340 is lowered into spotting fluid 330 in the lowerend of the wellbore 305. The float valve 355 should prevent entry of thespotting fluid 330 into the casing string 340. As the casing string 340is lowered into wellbore 305, the spotting fluid 330 may be displacedfrom the middle of the wellbore 305 by the casing string 340 with theannulus 335 surrounding the casing string 340 containing the spottingfluid 330. The spotting fluid 330 may be forced up the annulus 335causing the spotting fluid 330 to displace any other fluids (e.g.,drilling fluid 310 (as shown in FIGS. 5A and 5B) and/or any other fluidssuch as other treatment fluids) that may have remained in the wellbore305. If desired, the casing string 340 may then be suspended in thewellbore 305 until the spotting fluid 330 disposed in the annulus 335has set into a hardened mass. As discussed above, setting of thespotting fluid 330 may be induced through contact with a cement setactivator.

The exemplary treatment fluids disclosed herein may directly orindirectly affect one or more components or pieces of equipmentassociated with the preparation, delivery, recapture, recycling, reuse,and/or disposal of the disclosed treatment fluids. For example, thedisclosed treatment fluids may directly or indirectly affect one or moremixers, related mixing equipment, mud pits, storage facilities or units,composition separators, heat exchangers, sensors, gauges, pumps,compressors, and the like used generate, store, monitor, regulate,and/or recondition the exemplary treatment fluids. The disclosedtreatment fluids may also directly or indirectly affect any transport ordelivery equipment used to convey the treatment fluids to a well site ordownhole such as, for example, any transport vessels, conduits,pipelines, trucks, tubulars, and/or pipes used to compositionally movethe treatment fluids from one location to another, any pumps,compressors, or motors (e.g., topside or downhole) used to drive thetreatment fluids into motion, any valves or related joints used toregulate the pressure or flow rate of the treatment fluids, and anysensors (i.e., pressure and temperature), gauges, and/or combinationsthereof, and the like. The disclosed treatment fluids may also directlyor indirectly affect the various downhole equipment and tools that maycome into contact with the treatment fluids such as, but not limited to,wellbore casing, wellbore liner, completion string, insert strings,drill string, coiled tubing, slickline, wireline, drill pipe, drillcollars, mud motors, downhole motors and/or pumps, cement pumps,surface-mounted motors and/or pumps, centralizers, turbolizers,scratchers, floats (e.g., shoes, collars, valves, etc.), logging toolsand related telemetry equipment, actuators (e.g., electromechanicaldevices, hydromechanical devices, etc.), sliding sleeves, productionsleeves, plugs, screens, filters, flow control devices (e.g., inflowcontrol devices, autonomous inflow control devices, outflow controldevices, etc.), couplings (e.g., electro-hydraulic wet connect, dryconnect, inductive coupler, etc.), control lines (e.g., electrical,fiber optic, hydraulic, etc.), surveillance lines, drill bits andreamers, sensors or distributed sensors, downhole heat exchangers,valves and corresponding actuation devices, tool seals, packers, cementplugs, bridge plugs, and other wellbore isolation devices, orcomponents, and the like.

EXAMPLES

To facilitate a better understanding of the present claims, thefollowing examples of certain aspects of the disclosure are given. In noway should the following examples be read to limit, or define, theentire scope of the claims.

Example 1

A treatment fluid sample was obtained which comprised about 40% to about70% calcium aluminate cement by weight, about 33% to about 200% water byweight, about 0.01% to about 10% cement set retarder by weight, andabout 0.01% to about 5% dispersant by weight. In the examples, the terms“by weight” or “by wt.” refers to by weight of the treatment fluid. Thetreatment fluid was obtained from Kerneos, Inc., Chesapeake, Va.; as aretarded calcium-aluminate system comprising a suspension ofcalcium-aluminate cement that was 40-70% solids. The calculated densityof the treatment fluid was 14.68 ppg.

The apparent viscosities and FYSA decay readings of the sample wasmeasured at Day 0 and after storage at DAY 48 using a Model 35A FannViscometer and a No. 2 spring with a Fann Yield Stress Adapter (FYSA),in accordance with the procedure set forth in API RP Practice 10B-2,Recommended Practice for Testing Well Cements. The data is presented inTable 1 below.

TABLE 1 Treatment Fluid Rheological Profile FYSA Readings 3 6 100 200300 600 3D 6D Day 0 17759 10212 1305 839 666 506 7 4 Day 48 16871 97681265 806 644 506 5.5 5.5 Day 181 32411 18647 2464 1598 1261 901 13 11

As shown by these measurements, the slurry rheology remained stable forat least 48 days with little to no change in the calculated apparentviscosity. No settling of solids or free fluid was observed in thesamples over the test period further supporting the high degree ofslurry stability. At 181 days, there was no settling or free fluid eventhough the apparent viscosity had increased. Any gel that had formed,and which contributed to the increased viscosity, was easily broken uponstirring to return the slurry back to a flowable, pourable slurry.

Example 2

Another sample identical to that used in Example 1 was stored for 5months. After storage the apparent viscosities and FYSA decay readingsof the sample were measured over a 17 day period in the same manner asdescribed in Example 1. The data is presented in Table 2 below.

TABLE 2 Treatment Fluid Rheological Profile FYSA Readings 3 6 100 200300 600 3D 6D Day 0 14507 8387 1088 680 526 372 3.0 3.0 Day 3 11787 81601061 666 517 367 3.0 3.5 Day 5 14507 8613 1115 707 553 431 3.0 2.5 Day 711787 8160 1088 694 549 422 3.0 3.0 Day 10 14507 8613 1088 687 549 4223.5 3.0 Day 12 14053 8160 1088 687 539 417 2.5 3.0 Day 14 14507 83871088 687 549 417 2.5 2.5 Day 17 13147 8160 1088 687 539 408 2.0 3.0

Despite storing the treatment fluid for 5 months, the slurry rheologyremained stable with little to no change in the calculated apparentviscosity. No settling of solids or free fluid was observed in thesamples over the test period as well as after a further 4 months ofstorage further supporting the high degree of slurry stability.

Example 3

Four samples identical to that used in Examples 1 and 2 were activatedby the addition of a 4M NaOH (aq.) solution. The thickening times of thefour samples and a control sample were measured on a high-temperaturehigh-pressure consistometer by ramping from room temperature (e.g.,about 70° F. for this example) and ambient pressure to 100° F. and 3000psi in 15 minutes in accordance with the procedure for determiningcement thickening times set forth in API RP Practice 10B-2, RecommendedPractice for Testing Well Cements, First Edition, July 2005. Thethickening time is the time for the treatment fluid to reach 70 Bc andmay be reported as the time to reach 70 Bc. Additionally the pH of eachsample was measured after each sample had been activated. The results ofthis test are set forth below in Table 3.

TABLE 3 Treatment Fluid Thickening Time Measurements Cement SetActivator Amount Thickening Time (% by wt.) (hrs.) pH 4 2 12.3 2 6 10.61.5 19  9.6 1 190+  8.5 0 — 6.3

It was discovered that control over thickening times may be achieved byvarying the concentration of the activator. The results indicate adependence on concentration of the activator and the pH of the activatedtreatment fluid.

Example 4

A sample identical to that used in Examples 1 and 2 was activated by theaddition of a 1% by weight 4M NaOH (aq.) solution. The sample was splitinto four separate experimental samples and the thickening times of thefour samples were measured on a high-temperature high-pressureconsistometer by ramping from room temperature (e.g., about 70° F. forthis example) and ambient pressure to a temperature of either 100° F.,140° F., 180° F., or 220° F. in 15 minutes, 35 minutes, 55 minutes, or75 minutes respectively (i.e. a ramp of 2° F./min.), while holding thepressure constant at 3000 psi; in accordance with the procedure fordetermining cement thickening times set forth in API RP Practice 10B-2,Recommended Practice for Testing Well Cements, First Edition, July 2005.The thickening time is the time for the treatment fluid to reach 70 Bcand may be reported as the time to reach 70 Bc. The results of this testare set forth below in Table 4.

TABLE 4 Treatment Fluid Thickening Time Measurements TemperatureThickening Time Sample (° F.) (hrs.) A 100 190+   B 140 47.25 C 18020.25 D 220 11  

The results illustrate that the thickening times are dependent upontemperature, however, the effect of temperature does not appear toeffect the thickening times in a significant manner unless thetemperature is greater than 100° F. Thus, for uses of the treatmentfluids at temperatures greater than 100° F., the temperature must beconsidered when calculating thickening times.

Example 5

A sample identical to that used in Examples 1 and 2 was activated by theaddition of a 2% by weight 4M NaOH (aq.) cement set activator solution.The sample was split into three separate experimental samples. A lithiumsalt (Li₂CO₃) cement set accelerator was added to experimental sample Fin an amount of 0.5% by weight as cement set accelerator A. A differentlithium salt (Li₂SO₄.H₂O) cement set accelerator was added toexperimental sample G in an amount of 0.5% by weight as cement setaccelerator B.

The two experimental samples were then split further so that their 24hour compressive strengths could be measured at varying temperature. Thesamples were cured in 2″ by 4″ plastic cylinders that were placed in awater bath at 140° F. for 24 hours to form set cylinders. Then, thedestructive compressive strength (C.S.) was measured using a TiniusOlsen mechanical press in accordance with API RP Practice 10B-2,Recommended Practice for Testing Well Cements. The reported compressivestrengths are an average for two cylinders of each sample. Compressivestrength measurements were taken at 24 hours.

The thickening times of each sample was also measured on ahigh-temperature high-pressure consistometer by ramping from roomtemperature (e.g., about 70° F. for this example) and ambient pressureto 100° F. and 3000 psi in 15 minutes in accordance with the procedurefor determining cement thickening times set forth in API RP Practice10B-2, Recommended Practice for Testing Well Cements, First Edition,July 2005. The thickening time is the time for the treatment fluid toreach 70 Bc and may be reported as the time to reach 70 Bc. The resultsof these tests are set forth below in Table 5.

TABLE 5 Treatment Fluid Thickening Time Measurements Sample E Sample FSample G Compositional Makeup Cement Set Activator 2% by wt.   2% by wt.  2% by wt. Cement Set Accelerator A — 0.5% by wt. — Cement SetAccelerator B — — 0.5% by wt. pH Before Activation 6.3 6.3 6.3 AfterActivation 10.91 10.91 10.91 Compressive Strength (psi) 140° F. 463.41516.1 1815.2 Thickening Time (hh:mm) 6:00 5:15 —

The results illustrate that the addition of a lithium salt improvescompressive strength of a treatment fluid for the temperature rangetested without decreasing the thickening time by a substantial degree.Without being limited by theory, it is believed that lithium sulfatemonohydrate may have provided better compressive strength results due toits greater solubility in water. Additionally, the addition of a lithiumcarbonate reduced the thickening time by only 45 minutes while stillshowing a large compressive strength development relative to the controlSample A which did not include a lithium salt. Such a resultdemonstrates “right-angle” set behavior.

As described above, some of the treatment fluids may exhibit“right-angle” set behavior such that the slurry consistency remains low,for example, less than 30 Bc, until the thickening time is reached atwhich point the slurry rapidly gains high levels of strength. Therefore,some formulations of the treatment fluids may also mitigate gelation andprovide a treatment fluid that remains fluid for an extended period oftime up until a specific point in which it undergoes a near immediateset, thus reducing concerns over the treatment fluid gelling or settingwhile operations are ongoing, for example, while drilling if thetreatment fluid is being used as a drilling fluid. FIG. 7 provides anexample of “right-angle” set profile using Sample B from Example 4.

The preceding description provides various embodiments of the systemsand methods of use disclosed herein which may contain different methodsteps and alternative combinations of components. It should beunderstood that, although individual embodiments may be discussedherein, the present disclosure covers all combinations of the disclosedembodiments, including, without limitation, the different componentcombinations, method step combinations, and properties of the system. Itshould be understood that the compositions and methods are described interms of “comprising,” “containing,” or “including” various componentsor steps, the compositions and methods can also “consist essentially of”or “consist of” the various components and steps. Moreover, theindefinite articles “a” or “an,” as used in the claims, are definedherein to mean one or more than one of the element that it introduces.

For the sake of brevity, only certain ranges are explicitly disclosedherein. However, ranges from any lower limit may be combined with anyupper limit to recite a range not explicitly recited, as well as, rangesfrom any lower limit may be combined with any other lower limit torecite a range not explicitly recited, in the same way, ranges from anyupper limit may be combined with any other upper limit to recite a rangenot explicitly recited. Additionally, whenever a numerical range with alower limit and an upper limit is disclosed, any number and any includedrange falling within the range are specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues even if not explicitly recited. Thus, every point or individualvalue may serve as its own lower or upper limit combined with any otherpoint or individual value or any other lower or upper limit, to recite arange not explicitly recited.

Therefore, the present embodiments are well adapted to attain the endsand advantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, and may bemodified and practiced in different but equivalent manners apparent tothose skilled in the art having the benefit of the teachings herein.Although individual embodiments are discussed, the disclosure covers allcombinations of all of the embodiments. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. Also, the terms in the claimshave their plain, ordinary meaning unless otherwise explicitly andclearly defined by the patentee. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered ormodified and all such variations are considered within the scope andspirit of those embodiments. If there is any conflict in the usages of aword or term in this specification and one or more patent(s) or otherdocuments that may be incorporated herein by reference, the definitionsthat are consistent with this specification should be adopted.

What is claimed is:
 1. A system for treating a well comprising: atreatment fluid comprising a suspension of about 40% to about 70%calcium-aluminate cement by weight of the treatment fluid, wherein thetreatment fluid further comprises about 70% to about 200% water byweight of the calcium aluminate cement, about 0.01% to about 5%dispersant by weight of the calcium aluminate cement, and about 0.01% toabout 10% cement set retarder by weight of the calcium aluminate cement,wherein the treatment fluid is capable of remaining in a pumpable fluidstate for at least 7 days; a vessel to contain the treatment fluid; apumping system coupled to the vessel to pump the treatment fluid; adrilling system comprising a drill string, wherein the drilling systemis configured for circulation of the treatment fluid therethrough whileextending a wellbore through a subterranean formation using the drillstring; a conduit coupled to the pumping system; and a treatment fluidrecovery system for recovery of at least a portion of the treatmentfluid from the wellbore, wherein the treatment fluid recovery systemcomprises a vessel to store and mix a cement set activator with the atleast a portion of the treatment fluid to form an activated cement, andwherein the pumping system is further configured to pump the activatedcement into the wellbore.
 2. The system of claim 1 further comprising astorage system or storing the treatment fluid.
 3. The system of claim 1wherein the cement set retarder is selected from the group consisting ofhydroxycarboxylic acids or their respective salts, boric acid or itsrespective salt, and any combination thereof.
 4. The system of claim 1wherein the treatment fluid further comprises a cement set activator isselected from the group consisting of Groups IA and IIA hydroxides;alkaline aluminates; Portland cement, and combinations thereof.
 5. Thesystem of claim 1 wherein the dispersant is selected from the groupconsisting of sulfonated-formaldehyde-based dispersant, apolycarboxylated ether dispersant, and any combination thereof.
 6. Thesystem of claim 1 wherein the treatment fluid further comprises a cementset accelerator selected from the group consisting of lithium sulfate,lithium carbonate, and any combination thereof.
 7. The system of claim 1wherein at least a portion of the treatment fluid is allowed to remainstatic in the wellbore.
 8. The system of claim 1 wherein the treatmentfluid forms a puddle in the bottom of the wellbore.
 9. The system ofclaim 8 wherein the conduit is configured for placement into the puddleformed by the treatment fluid in the bottom of the wellbore.
 10. Asystem for treating a well comprising: a vessel containing a treatmentfluid comprising: a suspension of about 40% to about 70%calcium-aluminate cement by weight of the treatment fluid, about 70% toabout 200% water by weight of the calcium aluminate cement, about 0.01%to about 5% dispersant by weight of the calcium aluminate cement, andabout 0.01% to about 10% cement set retarder by weight of the calciumaluminate cement, wherein the treatment fluid is capable of remaining ina pumpable fluid state for at least 7 days to contain the treatmentfluid; a pumping system coupled to the vessel to pump the treatmentfluid, wherein the pumping system is configured to pump the treatmentfluid into a wellbore; and a treatment fluid recovery system forrecovery of at least a portion of the treatment fluid from the wellbore,wherein the treatment fluid recovery system comprises a vessel to storeand mix a cement set activator with the at least a portion of thetreatment fluid to form an activated cement, and wherein the pumpingsystem is further configured to pump the activated cement into thewellbore.
 11. The system of claim 10 wherein the cement set retarder isselected from the group consisting of hydroxycarboxylic acids or theirrespective salts, boric acid or its respective salt, and any combinationthereof.
 12. The system of claim 10 wherein the cement set activator isselected from the group consisting of Groups IA and IIA hydroxides;alkaline aluminates; Portland cement, and combinations thereof.
 13. Thesystem of claim 10 wherein the dispersant is selected from the groupconsisting of sulfonated-formaldehyde-based dispersant, apolycarboxylated ether dispersant, and any combination thereof.
 14. Thesystem of claim 10 wherein at least a portion of the treatment fluid isallowed to remain static in the wellbore.
 15. The system of claim 10wherein the treatment fluid forms a puddle in the bottom of thewellbore.
 16. The system of claim 10 further comprising a conduitcoupled to the pumping system.
 17. The system of claim 16 wherein theconduit is configured for placement into the puddle formed by thetreatment fluid in the bottom of the wellbore.
 18. The system of claim10 further comprising a drilling system comprising a drill string. 19.The system of claim 18 wherein the drilling system is configured forcirculation of the treatment fluid therethrough while extending awellbore through a subterranean formation using the drill string.